407
coast. Further, white bands of coral in the southern sector, at a height of 8 m above the present
water level, show that the area was once marine
and that the water was much deeper than present
depth. The chronological development of the
outer barrier spit of the lake has been dated by
optically stimulated luminescence studies of
minerals.
Hydrology
The infl ow of FW during the monsoon and of
seawater during the dry season alternately dominates the environment. This results in annual
cyclic changes in salinity from 1.8 to 2.0 ppt
(during monsoon) to 34–35 ppt (during summer).
Three hydrological subsystems control the
hydrology of the lake, namely , (a) the land-based
system comprising distributaries of the Mahanadi
River on the northern side, (b) 52 river channels
from the western side and (c) the Bay of Bengal
on the eastern side. Two of the three southern
branches of the River Mahanadi that trifurcate at
Cuttack feed the lake. Sixty-one percent
(850 m
3 /s) of the total freshwater infl ow into the
lake is contributed by these two branches. Further,
the rivers Kansari, Kusumi, Janjira and Tarimi
contribute to 39 % (536 cubic m
3
/s) as part of
another drainage system. The annual total surface
freshwater input to the lake is estimated to
1.76 km
3 including direct precipitation over the
lake contributing to 0.87 km
3 . The drainage basin
area of Chilika Lake has a tropical monsoon climate with an annual rainfall of 1,200–1,600 mm.
The lake experiences southwest and northeast
monsoons during June to September and
November to December, respectively, with average annual rainfall of 1,238.8 mm with approx.
72 rainy days.
Water Quality
Limnological analyses done by the Chilika
Development Authority (CDA) revealed that,
generally, (a) the maximum water temperature of
39.9 °C and minimum temperature of 14 °C, (b)
water pH 7.1–9.6, (c) transparency 9–155 cm and
(d) salinity 0–42 ppt show wide temporal and
spatial variation due to a complex blend of freshwater discharge, evaporation, wind condition and
tidal infl ow of seawater. Further, the brackish
nature of the lake is depicted by the record of 0
ppt near the mouth of Daya River and hypersaline
level of 42 ppt in the outlet channel during the
dry period, (e) DO 3.3–18.9 mg/l, (f) phosphate
phosphorus 0–0.4 ppm, (g) nitrate nitrogen
10–60 ppm and (h) silicates 1–8 ppm.
Sediment Characteristics
1. Adverse tidal exchange occurs usually due to
the littoral drift along the coastline. This
causes fl ow reduction and shifting of the lake
mouth every year. Estimated sediment transport due to this is of the order of 100,000 metric tonnes. This adverse effect needs
ameliorative actions.
2. Study of sediment cores indicated spatial variation of sedimentation rate in three zones of
the lake, namely , 7.6 mm/year in northern sector, 8.0 mm/year in central sector and 2.8 mm/
year in southern sector. The lake has comparatively higher sedimentation rate in northern
and central sectors and a slow rate in the
southern sector.
Conservation, Threats and Management
Conservation
In 1981, Chilika Lake was designated as the fi rst
Indian Ramsar wetland mainly on the basis of the
following: (a) >1 million migratory waterfowls
and shorebirds wintering here; (b) >400 vertebrate species recorded; (c) supporting a unique
assemblage of marine, brackish and freshwater
species as an estuarine lagoon; (d) occurrence of
several rare and endangered species of biota; and
(e) rich fi sh fauna supporting livelihood of the
community.
Threats
Some of these are as follows: (a) increased siltation due to littoral drift and sedimentation from
the inland river systems (concomitantly, there is
decreasing salinity and rapid expansion of
Potamogeton weeds), (b) shrinkage of water surface area, (c) choking of the inlet channel and
shifting of the mouth connecting the sea, (d)
decrease in salinity and fi sh resources, (e) proliferation of freshwater invasive species, (f) gradual
declining trend in productivity affecting livelihood,
(g) confl icts between fi shermen and non-fi shermen
20.3 Wetlands of Other Regions in India
coast. Further, white bands of coral in the southern sector, at a height of 8 m above the present
water level, show that the area was once marine
and that the water was much deeper than present
depth. The chronological development of the
outer barrier spit of the lake has been dated by
optically stimulated luminescence studies of
minerals.
Hydrology
The infl ow of FW during the monsoon and of
seawater during the dry season alternately dominates the environment. This results in annual
cyclic changes in salinity from 1.8 to 2.0 ppt
(during monsoon) to 34–35 ppt (during summer).
Three hydrological subsystems control the
hydrology of the lake, namely , (a) the land-based
system comprising distributaries of the Mahanadi
River on the northern side, (b) 52 river channels
from the western side and (c) the Bay of Bengal
on the eastern side. Two of the three southern
branches of the River Mahanadi that trifurcate at
Cuttack feed the lake. Sixty-one percent
(850 m
3 /s) of the total freshwater infl ow into the
lake is contributed by these two branches. Further,
the rivers Kansari, Kusumi, Janjira and Tarimi
contribute to 39 % (536 cubic m
3
/s) as part of
another drainage system. The annual total surface
freshwater input to the lake is estimated to
1.76 km
3 including direct precipitation over the
lake contributing to 0.87 km
3 . The drainage basin
area of Chilika Lake has a tropical monsoon climate with an annual rainfall of 1,200–1,600 mm.
The lake experiences southwest and northeast
monsoons during June to September and
November to December, respectively, with average annual rainfall of 1,238.8 mm with approx.
72 rainy days.
Water Quality
Limnological analyses done by the Chilika
Development Authority (CDA) revealed that,
generally, (a) the maximum water temperature of
39.9 °C and minimum temperature of 14 °C, (b)
water pH 7.1–9.6, (c) transparency 9–155 cm and
(d) salinity 0–42 ppt show wide temporal and
spatial variation due to a complex blend of freshwater discharge, evaporation, wind condition and
tidal infl ow of seawater. Further, the brackish
nature of the lake is depicted by the record of 0
ppt near the mouth of Daya River and hypersaline
level of 42 ppt in the outlet channel during the
dry period, (e) DO 3.3–18.9 mg/l, (f) phosphate
phosphorus 0–0.4 ppm, (g) nitrate nitrogen
10–60 ppm and (h) silicates 1–8 ppm.
Sediment Characteristics
1. Adverse tidal exchange occurs usually due to
the littoral drift along the coastline. This
causes fl ow reduction and shifting of the lake
mouth every year. Estimated sediment transport due to this is of the order of 100,000 metric tonnes. This adverse effect needs
ameliorative actions.
2. Study of sediment cores indicated spatial variation of sedimentation rate in three zones of
the lake, namely , 7.6 mm/year in northern sector, 8.0 mm/year in central sector and 2.8 mm/
year in southern sector. The lake has comparatively higher sedimentation rate in northern
and central sectors and a slow rate in the
southern sector.
Conservation, Threats and Management
Conservation
In 1981, Chilika Lake was designated as the fi rst
Indian Ramsar wetland mainly on the basis of the
following: (a) >1 million migratory waterfowls
and shorebirds wintering here; (b) >400 vertebrate species recorded; (c) supporting a unique
assemblage of marine, brackish and freshwater
species as an estuarine lagoon; (d) occurrence of
several rare and endangered species of biota; and
(e) rich fi sh fauna supporting livelihood of the
community.
Threats
Some of these are as follows: (a) increased siltation due to littoral drift and sedimentation from
the inland river systems (concomitantly, there is
decreasing salinity and rapid expansion of
Potamogeton weeds), (b) shrinkage of water surface area, (c) choking of the inlet channel and
shifting of the mouth connecting the sea, (d)
decrease in salinity and fi sh resources, (e) proliferation of freshwater invasive species, (f) gradual
declining trend in productivity affecting livelihood,
(g) confl icts between fi shermen and non-fi shermen
20.3 Wetlands of Other Regions in India